The present invention relates in general to the field of maintaining solid and liquid materials at a given temperature relative to a different temperature environment by means of thermally insulating the material in an insulated container. A more specific application of the instant invention relates to the field of maintaining food or beverages at a relatively constant temperature by minimizing thermal losses.
Prior art indicates that for a considerable length of time cylindrical vacuum insulated bottles commonly referred to as Thermos bottles have been utilized to maintain foods and beverages at an initial temperature, either hot or cold. Typically, these containers had a double-walled filler with the space between the walls being evacuated for insulation and mounted within a jacket which provided both additional exterior insulation and protection for the filler. The following United States patents are cited as representative of this type of construction: U.S. Pat. Nos. 3,845,873; 3,910,441; 3,961,720.
Although cylindrical Thermos bottles offer a convenient shape for handling, the cylindrical shape is inferior to that of a spherical container in several respects. A spherical container requires less surface area to enclose a given volume of liquid than does a cylinder. Thus, if a cylinder and a sphere were constructed from equal amounts of material, the sphere would contain a greater volume than would the cylinder. Therefore, to construct a container capable of storing a given volume the use of a spherical shape reduces the amount of material needed as compared with a cylindrical shape. Economy of manufacture is thus enhanced by the use of a spherical container.
The rate of heat loss is directly proportional to the surface area of the container. For a given volume of liquid to be stored, the container having the smallest surface area containing that liquid will provide the smallest heat loss. This, of course, assumes that materials having equal thermal insulating properties are used. Since the sphere offers the smallest surface area container to store a given volume of liquid, it, therefore, follows that a sphere will exhibit a smaller heat loss than would a cylindrical container made of material having equal thermal insulating properties. This means that such a spherical container after a given length of time would maintain its contents more closely to the initial temperature of the contents than would a cylindrical container. Thus, the sphere offers thermal advantages when compared to cylindrical containers.
Another advantage of the sphere is its ability to withstand pressure better than other shapes. The ability to withstand pressure becomes an increasingly important factor as the container size increases. Because a vacuum exists in the chamber between filler walls, atmospheric pressure exerts a force tending to collapse these walls towards each other. Pressure is defined as a force acting upon a given area. Therefore, the total force acting upon the filler walls increases proportionately as the filler surface area increases. A spherical container will therefore be subjected to less total force for a given volume than will a cylindrical container; This follows since the sphere has less surface area as discussed previously.
Another property of the sphere is its ability to withstand large forces normal to its surface without deformation. A larger force normal to the surface of a sphere is required for surface deformation than for the same force applied to a plan constructed of the same material. Similarly, the sphere offers greater resistance to deformation than does a cylinder because a sphere has a radius of curvature in both a horizontal and vertical plane as compared with the cylinder having only a radius of curvature in the horizontal plane. Thus, the spherical vacuum container has an advantage over the cylindrical vacuum bottle in its ability to withstand pressure.
Despite the above advantages, it is not as convenient to pour liquids from the mouth of a spherical container as from one of a conventional cylindrical shape. This is a significant consideration with containers intended for consumer use. A pump dispenser overcomes this disadvantage by eliminating the requirement of tipping a spherically shaped container to dispense liquids.
It is an object of the present invention to provide a substantially spherical vacuum container capable of withstanding greater pressure than cylindrical Thermos bottles.
Additional objects and features of the instant invention include:
(a) economy of material is achieved since less material is needed to construct the instant container; PA1 (b) less heat loss is achieved as compared with a cylindrical container of comparable material; PA1 (c) a given amount of liquid is stored in a smaller volume; PA1 (d) the construction of larger sizes is simplified due to the pressure withstanding properties of the instant invention; and PA1 (e) liquids contained in the instant invention are easily and conveniently dispensed by means of a dispenser pump.
Other objects and advantages of the instant invention will be apparent from the concluding portion of this specification.